Review of the Truma Combi Water Heater-Furnace

Ah, the comforts of the recreational vehicle. Everyone loves a hot meal and a comfortable bed, but heating and hot water are two luxuries that really set tent camping apart from the RV. The propane furnace and propane water heater have long been the go-to appliances to provide these luxuries, yet each have their limitations when it comes to efficiency and size. Indeed, a quick look at any RV equipped with these two archaic appliances and you’ll notice that they take up a lot of space. This use of space isn’t an issue in larger recreational vehicles, like motorhomes and fifth wheels, but can be in smaller RVs like van conversions and truck campers. These appliances also use a lot of propane. That’s why we were excited when we first learned about the Truma Combi water heater and furnace. This versatile little unit not only can heat the air and water in your RV, but can do so with greater efficiency. This is a review of the Truma Combi Eco Plus model, which runs on both propane and 110 volts AC.

Truma Combi Background

The Truma Combi is made in Putzbrunn, Germany by Truma Corp. The company was founded in 1949 by Philipp Kreis and is named after U.S. President Harry S. Truman. Kreis’ company started with a simple gas lamp, but today his company has grown into the leading caravan/RV component supplier in Europe. In 1994, the company released it’s first combination water heater-furnace unit, called the Trumatic C, which was replaced by the better, more efficient Truma Combi in 2007. Today, the company makes four Combi models for RVs: the Eco, the Eco Plus, the Comfort, and the Comfort Plus. In 2013, Truma opened an office in Elkhart, Indiana in order to handle distribution and technical support here in the growing North American market.

Truma Combi Pros and Cons

Compared to the traditional American water heater and furnace, the pros of the Truma Combi Eco Plus are pretty significant. First, the dual capable unit takes up half the space since only one appliance is needed rather than two. This means smaller rigs—like vans and truck campers—can capitalize on the smaller appliance footprint by utilizing the extra space for more important things like storage and extra batteries. In fact, this is the main reason why we opted to have this unit installed in our new Bundutec Roadrunner truck camper. Second, the Truma Combi Eco Plus weighs only 37 pounds. The combined weight of your typical American 20,000 BTU furnace and American 6 gallon water heater is 56 pounds (32 pounds for the furnace and 24 pounds for the empty water heater). That’s a pretty significant savings in weight, especially in today’s truck camper where every pound matters.

Truma Combi exhaust vent (upper left) and access hatch

The Truma Combi offers additional benefits to the RV owner. The Truma Combi utilizes a two-burner flame, making it more efficient by providing two operating levels for heating hot water, Eco and High. Moreover, the furnace portion of the unit is much quieter compared to the traditional propane furnace when it operates (comparatively speaking, we’d have to say that the Truma Combi’s noise level is two-thirds less than an American furnace). Not only that, the heating elements of the Truma Combi are mounted outside the water tank not inside like the traditional water heater. If you’ve ever had to replace a corroded anode rod in a Surburban water heater, you’ll really appreciate this feature. Draining the Truma Combi’s 2.6 gallon water tank for winterizing is easier, too—all you have to do is flip a switch. Nice!

Are there any cons associated with the Truma Combi? Just two. As you’d expect for a high-tech item, the Truma Combi Eco Plus costs more than your typical American furnace and water heater with an $1,800 cost. Second, while the Eco Plus heats water wonderfully well, the furnace of the Eco Plus—which puts out 14,300 BTU’s—isn’t nearly as powerful as Suburban’s ubiquitous 20,000 BTU propane furnace. Because of this, heating the camper initially with the Truma Combi Eco Plus will take longer though Truma makes a more capable Combi Comfort Plus model that puts out a very respectable 20,400 BTUs.

Truma Combi Operation

The way the Truma Combi works is pretty neat. The unit consists of a burner tube in the middle, which is about the size and shape of a Pringle’s potato chip can, an aluminum heater exchanger wrapped around the burner, and a 2.6-gallon stainless steel water tank encased around the heat exchanger. Air is drawn internally into the exchanger via a fan, heated by the burner, and distributed to the RV via a maximum of four flexible ducts (our Roadrunner truck camper has three). The wall cowl and the furnace are connected by an ingenious duct in the exhaust venting system, which consists of an exhaust tube inside and a combustion air intake tube outside. Water is heated in the Combi’s 2.6-gallon stainless steel tank. This tank is less than half the size of American water heaters, but because it heats water so fast, the smaller tank really isn’t an issue. Just make sure you leave it on while showering.

Internal components of the Truma Combi.

In the furnace mode, the Truma Combi has an adjustable temperature range between 40 and 86 degrees F. The furnace automatically selects the proper operating level based on the difference between the temperature set at the control panel and the current room temperature. If there is any water in the 2.6-gallon water container, the water will be heated automatically as well. The water temperature, however, will not be regulated in the furnace mode, but will not exceed a maximum of 162 degrees F.

In the water heater mode, two temperatures can be selected “Eco” (104 degrees), and “High” (140 degrees). A “Boost” mode can also be selected at the control panel, which will override furnace heating until the set water temperature is reached. According to the operating manual, the hot water mode is ideal only if hot water is required. The lowest burner setting suffices for heating water. In this mode, the burner will switch off as soon as the water reaches the temperature selected on the control panel.

Truma Combi Control Panel. The lightning bolt and power plug icon indicate that the unit is also operating on 110 volts AC.
Truma Combi temperature probe.

Learning how to operate the Truma Combi via the control panel is fairly easy. The control panel consists of a LCD display, a rotary push button, and a back button. Display elements on the control panel consist of a status on top (the icons flash until the desired air or water temperature is reached), menu items below (which includes room temperature, water temperature, power source, and fan speed), a power supply display, and settings/values (these include clock, temperature, error codes, and display settings including temperature offset). The rotary push button is used to select menu items in the top and bottom and to adjust settings. Newer units are also iNet ready, meaning that the unit can be controlled via Bluetooth/SMS with the addition of the iNet box and required smartphone application.

The Truma Combi Eco Plus allows for the selection of three sources of power: Propane (gas), Electric (110 volts AC), and Mixed (propane and electric). Furthermore, two electric modes can be chosen: Electric 1 (850 watts 110 volts AC) and Electric 2 (1,700 watts 110 volts AC). Two mixed modes can be selected at the control panel as well: Mixed 1 (propane and Electric 1) and Mixed 2 (propane and Electric 2). In the Mixed Mode, propane is used until the desired temperature(s) is/are reached. Thereafter, the electrical input takes precedence over propane. The added benefit of either Mixed mode is that the unit will automatically switch over to the other source in the event one of the sources is interrupted.

Learning how to use the Truma Combi’s temperature offset is important. This setting may be needed because the probe is sometimes mounted in a warmer location than the control panel and will shut down earlier than needed. The way it works is pretty easy. Supposing the cabin temperature is set to 75 degrees. If we set the offset to -5 degrees (an offset between 0 and -10 degrees can be selected), the unit will actually shut off the furnace when it reaches 70 vice 75 degrees. Not all RV’s need to use this feature—ours included—but it’s important to know how it works and that it’s there in case you need it.

Owners of the Truma Combi should be familiar with four error codes. The E45H error code indicates the absence of a 110 volt AC input, which will only display when operating in either the Mixed or Electric modes, while the E212H error code indicates an empty propane tank. These are probably the most common error codes associated with the Truma Combi and are the one’s we’ve encountered the most since we’ve owned our camper. Additional error codes that the owner should be aware of include an empty water tank (E17H) and loss of 12 volt DC power (E255H). The latter error code can be especially useful in the event of over discharging the battery while camping off-grid.

Truma Combi Ducting

Like we said earlier, the Truma Combi is pretty efficient. The average 12 volt power consumption when operating the furnace on propane is only 1.6 amps, with a transient maximum of 6 amps when operating the unit on the “High” fan speed. When operating the water heater, the power consumption is even less at .9 amps. As for propane consumption, we don’t have any measurements to say that the Truma Combi is better than the typical American water heater and furnace. The consumption rate depends on so many things including ambient temperatures, the camper’s R-rating, and other variables which are difficult to quantify, but with the Truma Combi’s quick hot water heating cycle and lower 14,300 BTU rating, it certainly seems that the Truma uses less propane compared to other campers we’ve owned.

How Well it Works

As you’d expect for such a complex piece of engineering, there is a learning curve associated with the Truma Combi. It’s not overly complex, but it’s nowhere as simple as operating an American-made Suburban or Atwood water heater or furnace. Still, it wasn’t that bad—it took us about two weeks to learn all of the ins and outs associated with operating it. The control panel’s back button can really save you time during setup if you can remember to use it (we usually don’t).

Off-grid, we operate the unit on propane only, while Mixed 2 operation is used when we’re plugged into shore power at home. It’s been our experience that the water heater portion of the Combi heats water quickly and very efficiently—we usually have hot water within 20 minutes and when we say hot, we mean HOT. As for the furnace portion of the Truma Combi, we’ve been somewhat disappointed. The Eco Plus’ 14,300 BTU rating is a bit anemic for our size of camper, and like we said earlier, takes awhile for the truck camper to heat up initially. Indeed, the forced air provided by the unit on the “High” fan speed is sufficient in the main cabin, but barely detectable in the cabover. For those ordering a truck camper we recommend the more capable Truma Combi Comfort Plus, which boasts a more robust rating of 20,400 BTUs.

We’ve also discovered that the furnace portion of the Truma Combi is a bit temperamental when running on propane. We’ve learned through trial and error not to operate both the furnace and the water heater on the “High” setting during the night. The water heater simply takes up too much 12 volt power in the unit, which in turn greatly reduces the furnace’s fan speed to “Eco,” the lowest speed offered by the unit. Even worse, the furnace often won’t work when operating simultaneously with the water heater on “High.” Not good. Fortunately, there is a good work-around—just operate the furnace alone since operating it automatically heats the water as well.

Final Verdict

You’d think with the aforementioned issue that we’d be down on this product, but that isn’t the case. We love the Truma Combi’s small footprint and versatility and believe that it, along with similar products like the Alde hydronic water heater-furnace—also owned by Truma—will pretty much be standard in most recreational vehicles within 10 years. Change due to technological advancements sometimes takes years to happen, but once it’s made, it’s made for good. Sure, we’ve been a bit disappointed with the Truma Combi’s somewhat anemic furnace, but we have learned to compensate for it by simply using the fan speed “Boost” mode and by allowing more time for the camper to heat-up. Like any good product, you have to learn how it works and responds in all temperatures, elevations, and settings. The Truma Combi is no different. We do, however, recommend installing Truma’s larger Comfort Plus model in truck campers and travel trailers to put it on a more equal footing with American furnaces. What would we rate the Truma Combi Eco Plus unit? On a scale of 1 to 5 with 1 being the lowest and 5 being the highest, we give this amazing product an enthusiastic rating of 5 stars.

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About Mello Mike 564 Articles
Mello Mike is an Arizona native, author, and the founder of Truck Camper Adventure. He's been RV'ing since 2002, is a certified RVIA Level 1 RV Technician, and has restored several Airstream travel trailers. He currently rolls in a 2013 Ram 3500 with a 2021 Bundutec Roadrunner truck camper mounted on top. A communications expert, he retired from the U.S. Navy in 2004 as a CWO3 after 24 years, worked in project management, and now runs Truck Camper Adventure full-time. He also does some RV consulting, repairs, and inspections on the side.

8 Comments

  1. Hi Mike,
    I’ve been eagerly awaiting this review. With respect to the furnace operation, what are the coldest sustained or nighttime temperatures you’ve used it in? How do you find the interior furnace noise and balance of the heat throughout the cabin, given three heat outlets, particularly compared to a tradition furnace like in your Laredo?

    Thanks, Pete

    • Hi Pete, I can give you some insight of the low temperature capability of the Truma. My 2021 Bunduvry has one, we were in Raymond, Iowa for some warranty work and it was 14 degrees, snow on the ground. The Truma had no problem in keeping our camper toasty warm and as far as noise goes it’s so quiet that I would put my hand at the supply outlet to check if it was on! My rig had four supply outlets and did a pretty good job of spreading the heat around, as far as compared to the furnance in my old Lance 815 this Truma is light years ahead.

  2. I’ll add a “con” to the list. I can’t get one. In the US, you can only order this unit in select new campers. Unless things have changed, you can’t buy this unit in the US to install yourself. People in other countries can, but not US. I think there is a company in Canada that will sell you one, but I don’t think it is supported by Truma. It makes no sense to me.

    I think it’s a great unit, and I want one. But unless I buy a new camper from a manufacturer that offers them, I can’t have it. And I think that is BS. BS I say!! Especially when folks in Canada, Australia and the UK can buy the kit. The company gets a BIG thumbs down from me.

    Joel

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